Breeds...

A dog breed is a group of dogs that have very similar or nearly identical characteristics of appearance or behavior or, usually, both, primarily because they come from a select set of ancestors who had the same characteristics.

Dogs have been selectively bred for specific characteristics for thousands of years. Initially the selections would have centered on domestication and useful behavior such as hunting ability. Later, dogs were also selected for attractive and distinctive forms, resulting in a vast variety of types.

Purebreed

Many traditional dog breeds recognised by the main breed registries are said to be "purebred". Only individuals whose parentage consists only of other purebred examples of the breed are regarded as part of that breed. This concept has caused controversy both because of the difficulty of regulation and because of the possible genetic consequences of a limited population (inbreeding). Recent work has been done to genetically classify the various breeds, with some surprising results regarding the estimated age and interrelations of the breeds.